DVI and HDMI are essentially the same connection with different plugs (awaits the pedants going on about audio)
The only thing you can do is add a second graphics card to your computer, although from experience trying to run some things full screen on one screen while trying to do things on the other screens can be a nightmare (the full screen keeps switching back to windowed setting)
Also you are going to need a pretty hefty computer to run 3 displays without it starting to bog down.